Clown loach

Water parameters

Tolerated range for this species. Aim for the middle of each band rather than the extremes.

Tank and habitat

Substrate: sand.

Behavior

Plant interaction: may nibble soft.

Typically wild-caught; acclimate slowly.

Feeding

Omnivore with a strong appetite for meaty food. Sinking pellets, sinking wafers, frozen bloodworm, frozen brine shrimp, frozen mysis, and live food (blackworms, chopped earthworm, brine shrimp) are all taken eagerly. and records note that bladder snails (Physella acuta) and other pest snails are reliably eaten and the species is valued for snail control in planted tanks; ornamental snails (mystery, nerite, ramshorn) get the same treatment, so the species is not safe with snails the keeper wants to keep. Plant matter is accepted: blanched zucchini, cucumber, peas, occasional banana or fruit. Loaches feed on the bottom and need food that actually reaches the substrate before midwater fish intercept it; sinking pellets and frozen food are better than flake. The fish is greedy but characteristically hangs back during the initial feeding rush and works the substrate over methodically afterwards. Feed once or twice daily. Adult groups need substantial volumes; a group of five fish at 20 to 25 cm consumes more food than most community owners initially expect.

Compatibility

• Social. Solitary fish or pairs hide constantly, lose colour, and often refuse food; groups of five or more show natural behaviour and the species' signature side-resting habit
• Peaceful with mid-to-large community fish: rainbowfish, larger tetras, barbs, other loaches, congo tetras, non-aggressive cichlids. Despite the adult size, the species is not predatory toward fish
• Snails and shrimp are eaten. Bladder snails (Physella acuta) and other pest snails are cleared efficiently and the species is actively used for snail control in planted tanks. Ornamental snails (mystery, nerite, ramshorn, assassin) get the same treatment
• The most mis-sold large fish in the hobby. Stores routinely sell 4 to 5 cm juveniles to keepers with 75 to 150 litre tanks. Adults reach 20 to 30 cm over several years and need a group tank of 450 litres or more; many specimens stunt and die prematurely in tanks they were never going to fit in
• Bornean and Sumatran forms cross freely in captivity; locality-pure stock is worth keeping separated if regional bloodlines matter to the keeper

Origin and habitat

A large botiid loach endemic to Indonesia, on the Greater Sunda Islands of Sumatra and Borneo, and the sole member of the genus Chromobotia. The range covers river systems on Borneo across the three Indonesian Kalimantan provinces (Kalimantan Barat, Tengah, Timur), including the Kapuas and Kayan, and on Sumatra across the eastern and southern drainages of Jambi, Sumatera Selatan, and Lampung provinces, including the Batang Hari, Musi, and Tulang Bawang. Pieter Bleeker described the species in 1852 as Cobitis macracanthus; the type series came from Palembang and Kwanten in Sumatra (the latter probably the modern Kuantan Singingi area in Riau province, putting the type locality in the Indragiri River basin). The species was reclassified as Botia macracanthus in 1989. Maurice Kottelat then divided the 47-species Botia into seven genera in 2004 (Zootaxa 401:1-18, originally describing Botia kubotai), raising the new monotypic genus Chromobotia for this species. Botiidae itself was elevated from a subfamily of Cobitidae to a full family by Nalbant in 2002. The genus name combines Greek khroma (colour) with the regional Asian word Botia (warrior/soldier); the species epithet combines Greek makros (large) with Latin acanthus (thorny), referring to the prominent bifid subocular spine. That spine sits in a groove below each eye and can be erected defensively; it catches in fine-mesh nets and can pierce skin, so handlers use a rigid container. Adults are river-bottom fish that move seasonally: they migrate upstream to flooded forest during the wet season to spawn, while juveniles stay in vegetation-rich floodplains. Wild adults reach over 20 inches and are eaten locally as food fish; Records show 30.5 cm TL and 469 g for the largest specimen on record, taken from the Musi River. Captive specimens almost never reach full wild size, partly because of slow growth and partly because few aquarists keep them in tanks the size they actually need. Two regional forms exist. Bornean fish show black colouration through the pelvic fins (heavy in some individuals) and the rear black band extends onto the caudal peduncle. Sumatran fish have entirely reddish-orange pelvic fins and the rear band terminates closer to the body. A rare albino/platinum strain also turns up in the trade. Sexual dimorphism is subtle: females are slightly plumper, and males show tail tips that curve inward; FishiPedia describes no visible dimorphism. The local Sentarum name in West Borneo is ulanguli. The species clicks audibly with its pharyngeal teeth when feeding, displaying, or mating. It is scaleless and therefore more sensitive than scaled fish to medications, low water quality, and skin injuries; medications often need to be dosed at half strength. IUCN Least Concern (assessed 28 November 2019). The wild harvest of juveniles for the aquarium trade has reached tens of millions per year, and Indonesia issued a 2002 Decree forbidding export of any specimen over 15 cm to protect sexually mature spawners in the wild.

Breeding

Not bred in home aquariums. The species needs seasonal triggers (monsoon flooding, upstream migration to flooded forests, temperature and conductivity shifts) that a glass tank simply cannot reproduce, and every documented hobby attempt has failed. Sexual dimorphism is too subtle to reliably pair fish in any case: females are sometimes slightly plumper and males may have inward-curving tail tips, but the difference is inconsistent and FishiPedia records no visible dimorphism in many specimens. Commercial production happens in earthen ponds in Southeast Asia using hormone induction; a published patent (US 8,701,596) describes the procedure with GnRHa or LHRH-A in combination with the antidopaminergic drugs domperidone or pimozide, recycled water at controlled pH (7.0 to 8.0), conductivity (100 to 300 microsiemens), and oxygen, followed by larval rearing through to juvenile stage. Wild capture remains a significant proportion of the trade: industry observers report a steady decline in juvenile catch over almost 30 years despite increasing fishing intensity. The Indonesian 2002 Decree banning export of fish above 15 cm is aimed at protecting reproductive adults in the wild. Captive-bred farm stock is increasingly available and generally more robust than wild-caught specimens in the trade.

Common problems

Ich (Ichthyophthirius multifiliis) is the defining health risk and clown loaches are among the most ich-susceptible freshwater species in the trade. Outbreaks are nearly inevitable after purchase, transport, or any temperature drop. Treatment is complicated by scaleless skin, which absorbs medication faster than scaled fish; standard ich medications need to be dosed at roughly half strength or they burn the fish. Heat treatment (raising the tank to about 30 C for 10 to 14 days) is often safer than chemicals. The other persistent issue is stunting from inadequate tank size. The fish is sold at 3 to 5 cm and looks suited to a community tank, but adults reach 20 to 30 cm and a group needs a tank around 450 to 600 litres or larger; many specimens die prematurely in small tanks from chronic stress and stunted growth, which is probably the most regretted impulse buy in the hobby. The subocular spines catch in fine-mesh nets and can injure both the fish and the handler, so a rigid container is the only safe way to move them. Solitary clown loaches behave abnormally: constant hiding, faded colour, and refusal to eat are typical signs of insufficient group size, and groups of five or more keep the fish settled. The well-known habit of lying flat on the side is normal resting behaviour, not illness, and panics new owners regularly.

Bioload

Further reading

• How to cycle a fish tank
• Stocking ideas by tank size